FIG. 1 shows a hybrid fiber coaxial network including a CMTS and a CM for simultaneously transmitting and receiving data, respectively, through four downstream channels. As shown in FIG. 1, a classifier 111 of a CMTS 110 classifies packets received from a network-side interface (hereinafter, referred to as “NSI”) 140 into packets 115 for which resequencing is not necessary (hereinafter, referred to as “ordinary packets”) and packets 116 for which resequencing is necessary (hereinafter, referred to as “resequencing packets”). Among the classified packets, the ordinary packets 115 are transmitted to one or all of four schedulers 113. Whereas, the resequencing packets 116 are transmitted to a sequencer/distributor 112 and assigned numbers according to a resequence order. The resequencing packets 116 are then distributed to the four schedulers 113 in a specific manner.
Each scheduler 113 of the CMTS 110 receives the ordinary packets 115 or the resequencing packets 116 and transmits them to a CM 120 through one of the four downstream channels 114 based on a scheduling algorithm. The CM 120 processes the received packets and transmits them to a customer premises equipment (hereinafter, referred to as “CPE”) 130.
The CM 120 in a hybrid fiber coaxial network structure receives the ordinary packets 115, which are transmitted through a single downstream channel 114, and the resequencing packets 116, which are transmitted through two to four downstream channels 114. Therefore, the CM 120 is required to simultaneously process the ordinary packets 115 and the resequencing packets 116. In particular, since the resequencing packets 116 are distributed to two to four downstream channels 114 by the CMTS 110 to be transmitted therethrough, a receiving order of the packets at the CM 120 can be made to be different from a transmitting order thereof at the NSI 140 depending on settings of each scheduler 113 of the downstream channels 114 and each downstream channel 114. Therefore, in order to output the received resequencing packets in the same order as the input order from the NSI 140 to the CMTS 110, the CM 120 performs a packet resequencing process before transmission to the CPE 130.
The CMTS 110 transmits a downstream service identifier encoding information (hereinafter, referred to as “DSID”), which is necessary information for the CM 120 to process the ordinary packets 115 and the resequencing packets 116, to the CM 120 in the initialization process, and thereafter transmits the packets into which the DSID is inserted. When transmitting the resequencing packet the CMTS 110 inserts also a packet sequence number (hereinafter, referred to as “PSN”) for use in resequencing into the packet. The CM 120 processes downstream packets by using control information received from the CMTS 110 and information included in the packets.
The DSID encoding information that is transmitted from the CMTS 110 to the CM 120 in the initialization process includes individual DSID information to be received and processed by the CM 120; operation information for the DSID information; and information for use in identifying the ordinary packet and the resequencing packet. Particularly, the DSID of the resequencing packet further includes downstream resequencing channel list information and resequencing waiting time information.
FIGS. 2A to 2D show various formats of packets transmitted from the CMTS 110 to CM 120.
A first packet 201 is an ordinary unicast packet having no traffic priority. As shown in FIG. 2A, the packet 201 is formed of a MAC header 210 and a MAC data 220, wherein the MAC header 210 includes a frame control field (hereinafter, referred to as “FC”) 211 for indicating a packet type and existence of an extended header, a MAC parameter field (hereinafter, referred to as “MAC_PARM”) 212 for indicating a length of the extended header, a length field (hereinafter, referred to as “LEN”) 213 for indicating a total length of the packet, and a header check sequence field (hereinafter, referred to as “HCS”) for use in error checking of the MAC header 210.
A second packet 202 is an ordinary unicast packet having a traffic priority. As shown in FIG. 2B, the packet 202 additionally includes an extended MAC header field (hereinafter, referred to as “EHDR”) 215, wherein the EHDR 215 has traffic priority information indicating a traffic priority of the packet.
A third packet 203 is an ordinary multicast packet. As shown in FIG. 2C, the packet 203 additionally includes an EHDR 216. In comparison with the EHDR 215 of the unicast packet 202, the EHDR 216 of the multicast packet 203 additionally has DSID information for use in identifying the multicast packet 203.
A fourth packet 204 shown in FIG. 2D is a resequencing unicast/multicast packet. The packet 204 is formed by adding an EHDR 217 to the ordinary unicast packet 201, wherein, compared with the EHDR 216 of the ordinary multicast packet 203, the EHDR 217 additionally has a sequence change counter (hereinafter, referred to as “SCC”) value and PSN information in which enable a resequencing process.
The first to the third packets 201 to 203 are ordinary packets that is transmitted through a single channel, whereas the fourth packet 204 is the resequencing packet that is transmitted through a plurality of channels.
The CM 120 classifies such various types of packets into the ordinary packets and the resequencing packets based on their formats, and then processes and outputs them. In particular, in order to resequence the resequencing packets based on the PSN, the CM 120 needs to have a specific size of buffer for storing therein packets received from the CMTS 110 in the receiving order different from the transmitting order from the NSI 40 to the CMTS 110. Further, since the packets are outputted from an output end of the CM 120 one by one, a buffer space for temporarily storing therein the ordinary packets is also necessary.
As described above, since the CM 120 needs to store all the receiving packets, the size of the buffer required in the CM 120 depends on a packet arrival rate and a waiting time of the stored packet. Further, in case of separately providing a buffer for storing the ordinary packets and a buffer for storing the resequencing packets, there occurs a problem that the required buffer size increases significantly.